Ostwald ripening of spherical Fe particles in Cu-Fe alloys

The coarsening of spherical n -Fe and f -Fe precipitate particles in Cu-Fe alloys aged at 600, 650 and 700C has been studied by measuring both the particle size by transmission electron microscopy and the Fe concentration in the Cu matrix by electric resistivity. The average size of n -Fe and f -Fe particles increases with ageing time t as t 1/3, as predicted by the Lifshitz-Slyozov-Wagner theory. The kinetics of the depletion of supersaturation with t for n -Fe and f -Fe particles are consistent with the predicted t -1/3 time law. The solubilities of Fe in equilibrium with a n -Fe particle of infinite size are greater than those in equilibrium with an f -Fe particle of infinite size. The Fe-Cu interface energy and the diffusivity of Fe in Cu have been independently derived from the data on coarsening. The coherent n -Fe-Cu interface energy is estimated to be 0.25Jm -2, and the incoherent f -Fe-Cu interface energy 0.52Jm -2 . The preexponential factor and activation energy for diffusion are found to be 9.75 10 -5 m 2 s -1 and 213kJmol -1 respectively.     

Cooling-rate-dependent microstructure and mechanical properties of a CuZrAlAg alloy

A Cu₃₆Zr₄₈Al₈Ag₈ alloy rod with a diameter of 10 mm was fabricated using a copper-mould suction casting method. Structural characterization revealed that the rod has different microstructures along the casting direction, including a complete amorphous structure and an amorphous/crystalline composite structure with different amount of B2 CuZr phase. Nanoindentation tests showed that the hardness and the elastic modulus of the crystalline phase are lower than those of the amorphous matrix. The hardness and the elastic modulus of the amorphous matrix decrease with decreasing crystalline proportion of the alloy, while the Vickers hardness of the alloy increases with a reduction in the crystalline proportion.     

Nucleation of He bubbles in amorphous FeBSi alloy irradiated with He ions

It is interesting to investigate the formation of He bubbles in amorphous alloys because point defects do not exist in amorphous materials. In the present study, the microstructural evolution of amorphous Fe₇₉B₁₆Si₅ alloy, either irradiated with 5?keV He⁺ ions or implanted with 150?eV He⁺ ions without causing displacement damage, and then annealed at a high temperature, was investigated using transmission electron microscopy (TEM). Vacancy-type defects were formed in the amorphous alloy after irradiation with 5?keV He⁺ ions, and He bubbles formed during annealing the irradiated samples at high temperature. On the other hand, for samples implanted with 150?eV He⁺ ions, although He atoms are also trapped in the free volume, no He bubbles were observed during annealing the samples even up to 873?K. In conclusion, the formation of He bubbles is related to the formation and migration of vacancy-type defects even in amorphous alloys.     

Investigation of the interaction of He and D in FeBSi alloy

He and H can be produced by nuclear reaction. In addition, energetic particles of He and T and D, which are isotopes of H, in the plasma of fusion reactor induce the damage in the surface of materials, such as erosion, sputtering and blistering. To investigate the interaction of He and D, amorphous and crystalline FeBSi alloys were irradiated by He or D₂ or He?+?D₂ ions with 5?keV. The results of thermal desorption indicated that more He atoms were trapped in both the amorphous and crystalline alloy irradiated by He ions than D atoms in those alloys irradiated by D₂ ions. Although He and D atoms were trapped in FeBSi alloy irradiated by He?+?D₂ ions, desorption peaks of D₂ and He were separated. Absorption of D in an amorphous alloy was influenced by the presence of He; however, absorption of He was independent of D₂ irradiation in both alloys.     

Role of speechreading in audiovisual interactions during the recovery of speech comprehension in deaf adults with cochlear implants

Speechreading is an important form of communicative activity that improves social adaptation in deaf adults. Cochlear implantation allows interaction between the visual speechreading abilities developed during deafness and the auditory sensory experiences acquired through use of the cochlear implant. Crude auditory information provided by the implant is analyzed in parallel with conjectural information from speechreading, thus creating new profiles of audiovisual integration with implications for brain plasticity. Understanding the peculiarities of change in speechreading after cochlear implantation may improve our understanding of brain plasticity and provide useful information for functional rehabilitation of implanted patients. In this article, we present a generalized review of our recent studies and indicate perspectives for further research in this domain.     

Dominant factors influencing the nanoindentation response of piezoelectric materials: a case study in relaxor ferroelectrics

The nanoindentation response of a piezoelectric material is, in general, influenced in a complex manner by its elastic, dielectric and piezoelectric properties. The present study is focused on obtaining a comprehensive understanding of the dominant material factors influencing the force–depth mechanical indentation response and the charge–depth electrical indentation response of piezoelectric materials. From a large number of three-dimensional finite element simulations of the indentation of simple and complex piezoelectric materials (such as PZT-5A and relaxor ferroelectrics), the following principal conclusions are obtained: (1) For indentations with both conducting and insulating indenters, the mechanical indentation stiffness is influenced more by the elastic properties, while the electrical indentation stiffness is influenced largely by the piezoelectric properties of the indented materials. (2) For longitudinal indentations using a conducting indenter, the elastic constants, C ₃₃ and C ₁₃, and piezoelectric constants, e₃₃ and e₁₅, are, respectively, the first and second most dominant material constants that influence the mechanical indentation stiffness and the electrical indentation stiffness. (3) For transverse indentations using a conducting indenter, the elastic constants, C ₁₁ and C ₁₂, are, respectively, the first and second most dominant material constants that influence the mechanical indentation stiffness. (4) In the indentation of relaxor ferroelectrics based on PMN-xPT and PZN-xPT, which exhibit a range of elastic, dielectric and piezoelectric properties, it is generally observed that materials with higher normal elastic and piezoelectric constants, i.e., C ₃₃ and e₃₃, respectively, exhibit higher mechanical and electrical indentation stiffnesses.     

Effect of Nb on nanoquasicrystalline Al-based alloys

Nanoquasicrystalline Al-based alloys, containing icosahedral particles in an α-Al matrix, exhibit high strength at elevated temperature. The metastability of the quasicrystals can limit the use of these alloys. In the present work, the microstructural evolution of Al₉₃(Fe₃Cr₂)₇ and Al₉₃Fe₃Cr₂Nb₂ (at%) alloys was studied using heat treatments and structural characterization by XRD, TEM and STEM-EDX analysis. It was observed that the Nb is dissolved in the Al–Fe–Cr icosahedral phase. This provides higher thermal stability, retaining the fine nanoquasicrystalline microstructure for longer times at high temperature.     

Studies of interaction between He and elements with mass number 140 in Fe by time-differential perturbed-angular-correlation measurements

Room-temperature time-differential perturbed-angular-correlation (TDPAC) spectra of ¹⁴⁰Ce arising through ¹⁴⁰Ba-¹⁴⁰La from ¹⁴⁰Cs in He-doped Fe, unannealed and annealed in vacuum at various temperatures, were obtained in order to examine whether Ce (or rather, La and Ba) and He form complexes having a definite geometrical structure in Fe, as suggested by first-principles density-functional theory calculations. No clear signal of such complexes was observed in the TDPAC spectra. However, the TDPAC spectra indicate that Ce and He form complexes having a variety of geometrical structures. Comparison with reported TDPAC results on ¹¹¹Cd arising from ¹¹¹In in He-doped stainless steel shows that the parent atoms (La and Ba) of ¹⁴⁰Ce trap He atoms more efficiently than In atoms do, indicating stronger bonding of He to the former atoms, while different from the present case, ¹¹¹Cd (In)–He complexes form a unique geometrical structure.     

Effect of strain rate on the compressive behaviour of a Zr56Al10.9Ni4.6Cu27.8Nb0.7 bulk metallic glass

We report the study of the effect of strain rate on the compressive behaviour of a Zr₅₆Al_10.9Ni_4.6Cu_27.8Nb_0.7 bulk metallic glass. The results indicated that both the strength and plasticity of the glass increase with increasing the strain rate up to 10^?5 s^?1, above which the strength and plasticity start to decrease. The enhanced mechanical properties under a strain rate of 10^?5 s^?1 are due to the emission/propagation rate of the shear bands being consistent with the strain rate.     

Effect of neurofeedback on hemispheric word recognition

We applied SMR/theta neurofeedback (NF) training at central sites of 20 Israeli children aged 10-12 years, half boys and half girls. Half of the subjects received C3 training and the other half C4 training, consisting of 20 half-hour sessions. We assessed the effects of training on lateralized lexical decision in Hebrew. The lateralized lexical decision test reveals an independent contribution of each hemisphere to word recognition (Barnea, Mooshagian, & Zaidel, 2003). Training increased accuracy and sensitivity. It increased left hemisphere (LH) specialization under some conditions but it did not affect interhemispheric transfer. Training did affect psycholinguistic processing in the two hemispheres, differentially at C3 and C4. Training also increased hemispheric independence. There were surprising sex differences in the effects of training. In boys, C4 training improved LH accuracy, whereas in girls C3 training improved LH accuracy. The results suggest that the lateralized NF protocol activates asymmetric hemispheric control circuits which modify distant hemispheric networks and are organized differently in boys and girls.     

Grain orientation effects on dynamic strength of FCC multicrystals at low shock pressures: a hydrodynamic instability study

Variability in local dynamic plasticity due to material anisotropy in polycrystalline metals is likely to be important on damage nucleation and growth at low pressures. Hydrodynamic instabilities could be used to study these plasticity effects by correlating measured changes in perturbation amplitudes at free surfaces to local plastic behaviour and grain orientation, but amplitude changes are typically too small to be measured reliably at low pressures using conventional diagnostics. Correlations between strength at low shock pressures and grain orientation were studied in copper (grain size?≈?800 μm) using the Richtmyer–Meshkov instability with a square-wave surface perturbation (wavelength = 150 μm, amplitude = 5 μm), shocked at 2.7 GPa using symmetric plate impacts. A Plexiglas window was pressed against the peaks of the perturbation, keeping valleys as free surfaces. This produced perturbation amplitude changes much larger than those predicted without the window. Amplitude reductions from 64 to 88% were measured in recovered samples and grains oriented close to 〈0 0 1〉 parallel to the shock had the largest final amplitude, whereas grains with shocks directions close to 〈1 0 1〉 had the lowest. Finite element simulations were performed with elastic-perfectly plastic models to estimate yield strengths leading lead to those final amplitudes. Anisotropic elasticity and these yield strengths were used to calculate the resolved shear stresses at yielding for the two orientations. Results are compared with reports on orientation dependence of dynamic yielding in Cu single crystals and the higher values obtained suggest that strength estimations via hydrodynamic instabilities are sensitive to strain hardening and strain rate effects.     

非面孔物体倒置效应形成过程的认知神经机制

物体识别, 尤其是人造新异物体专家识别形成过程的神经机制是了解大脑可塑性的一个重要窗口。当前, 从行为学上或神经机制上探讨物体特定角度体验程度与物体专家识别形成关系的研究较少, 本项目采用事件相关电位与行为训练相结合的方法, 分别选择在社会生活中自然形成的某类物体识别专家和经人为训练形成的人造新异物体识别专家作为被试, 研究非面孔物体识别倒置效应从无到有、从小到大整个过程的脑机制。通过对倒置效应大小的操纵, 分离出专家识别状态下的ERP成分, 并分析专家识别形成过程的脑电动态变化过程, 探讨非面孔物体识别大脑可塑性变化的神经机制。在上述研究的基础上, 研究者试图提出物体特定角度体验程度与物体识别加工方式选择关系模型并完善当前物体识别整体布局加工连续量假设(configural processing continuum)理论。     

Impact resistance performance of diamond film on a curved molybdenum substrate

Diamond films with different thicknesses were deposited on flat and curved molybdenum substrate by the microwave plasma chemical vapour deposition (MPCVD) method. Scanning electronic microscopy, atomic force microscopy and Raman spectroscopy were employed to characterise the morphology, the surface roughness and the composition of the films, respectively. A NanoTest system was used for hardness, elastic modulus and nanoimpact tests. The curved surface and ductility of the molybdenum substrate allow large deformation for the thinner films. The substrate has less effect on impact for the thicker film, the deformation of which is mainly determined by the film composition. Under a load of 50 mN and 75 cycles, less deformation occurred for the 22 μm thick film on the curved molybdenum substrate.     

Interindividual Variability in Use-Dependent Plasticity Following Visuomotor Learning: The Effect of Handedness and Muscle Trained

Motor learning has been linked with increases in corticospinal excitability (CSE). However, the robustness of this link is unclear. In this study, changes in CSE associated with learning a visuomotor tracking task were mapped using transcranial magnetic stimulation (TMS). TMS maps were obtained before and after training with the first dorsal interosseous (FDI) of the dominant and nondominant hand, and for a distal (FDI) and proximal (biceps brachii) muscle. Tracking performance improved following 20 min of visuomotor training, while map area was unaffected. Large individual differences were observed with 18%–36% of the participants revealing an increase in TMS map area. This result highlights the complex relationship between motor learning and use-dependent plasticity of the motor cortex.     

Formation of metastable phase and its influence on the solidification microstructure of highly undercooled eutectic Fe40Ni40B20 alloy

Solidification of a highly undercooled eutectic Fe₄₀Ni₄₀B₂₀ alloy melt has been studied by high-speed video in combination with an analysis of the temperature history. The metastable phase with a colony shape structure solidified primarily from the melt. DSC analysis confirmed the formation of the metastable phase. The metastable phase was re-melted, transformed or decomposed into stable phases during further solidification or cooling processes, and gave birth to the final as-solidified structures. On this basis, the effects of the metastable phase formation and transformation on evolution of the as-solidified structure is described.     

Enhancement on the faceted growth and the coarsening of the MnBi primary phase during the directional solidification under a high magnetic field

The effect of a high magnetic field on the morphology of the MnBi primary phase during the directional solidification has been investigated experimentally and the results show that an application of a high magnetic field has enhanced the faceted growth and the coarsening of the MnBi primary phase. This may be attributed to the effect of a high magnetic field on the diffusion of the solute Mn and the growth anisotropy of the MnBi crystal.     

Effect of heat treatment on the microstructure and mechanical properties of spray-formed 7055 aluminium alloy

7055 Al alloys samples were prepared by spray forming and hot-extrusion followed by two different aging treatment procedures. Their different distributions of GP zones, and nanoscale precipitates η′ (MgZn) and η (MgZn₂) are extensively investigated by transmission electron microscope (TEM). The mechanical properties, including tensile strength, Vickers hardness and elongation of both aged 7055 Al alloys, have also been measured and analysed. It is found that T6 and T76 aging treatment results in quite different microstructure and mechanical properties. The outstanding performance of the 7055 Al alloys after T6 aging treatment is attributed to nanoscale semi-coherent dispersion precipitates.     

一氧化氮在新生儿缺氧缺血性脑病中的作用

在围产期窒息引起的新生儿缺氧缺血性脑病（HIE）中,一氧化氮（NO）对脑组织具有神经保护性和神经毒性双重效应,这取决于NO的来源。并且NO与谷氨酸及内皮素（ET）相互作用。应用哲学观点深入研究NO的作用机制对于探讨HIE的防治具有重要意义。     

Observation of Cu nanometre scale clusters formed in Fe85Si2B8P4Cu1 nanocrystalline soft magnetic alloy by a spherical aberration-corrected TEM/STEM

Microstructure of a nanocrystalline soft magnetic Fe₈₅Si₂B₈P₄Cu₁ alloy (NANOMET^®) was investigated by the state of the art spherical aberration-corrected TEM/STEM. Observation by TEM shows that the microstructure of NANOMET^® heat treated at 738 K for 600 s which exhibits the optimum soft magnetic properties has homogeneously distributed bcc-Fe nanocrystallites with the average grain size of 30 nm embedded in an amorphous matrix. Elemental mappings indicate that P is excluded from bcc-Fe grains and enriched outside the grains, which causes to retard the grain growth of bcc-Fe crystallites. The aberration-corrected STEM-EDS analysis with the ultrafine electron probe successfully proved that Cu atoms form nanometre scale clusters inside and/or outside the bcc-Fe nanocrystallites.